Electronics cabinet with an air-to-air heat exchanger mounted to the outside of the cabinet

ABSTRACT

An air-to-air heat exchanger is simply and easily installed in an electronics cabinet in the field by using a template to form an air exit opening that corresponds with an air inlet opening of the heat exchanger, and an air inlet opening that corresponds with an air exit opening of the heat exchanger. Once the openings have been formed, the heat exchanger is mounted to the outside of the cabinet, such as on a side wall or a door of the cabinet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electronics cabinets and, moreparticularly, to an electronics cabinet with an air-to-air heatexchanger mounted to the outside of the cabinet.

2. Description of the Related Art

Telecommunication equipment is commonly housed in electronics cabinetsthat sit outside in residential and commercial neighborhoods. Thecabinets are water tight and air tight to prevent water and dust fromentering the cabinets and reducing the useful life of the equipmentinside the cabinets.

FIG. 1 shows a perspective view that illustrates a prior-art electronicscabinet 100. As shown in FIG. 1, cabinet 100 includes a base plate 110,a top plate 112, and a number of side walls 114 that are connected tobase plate 110 and top plate 112. In addition, cabinet 100 includes arack 116 that holds telecommunication equipment, and a door 118 that isconnected to the side walls 114 via hinges or other rotational means toprovide access to the interior of cabinet 100.

One trend in the telecommunications industry is to make line replaceablecards such that, for example, a card that supports plain old telephoneservice (POTS) can be replaced with a card that supports both POTS andxDSL broadband data service. Replacement cards which provide more thanbasic POTS service, however, tend to generate more heat than basic POTScards.

Thus, as the power requirements of the replacement equipment increase,more and more heat must be removed from the enclosures where theequipment is housed. This is a particular problem for legacy electronicscabinets which were originally optimized for one heat load, but whichnow must manage the increased heat load that results from thereplacement equipment.

Since the enclosure is air tight and water tight, heat removal must takeplace through a boundary surface by using, for example, a heatexchanger. For legacy electronics cabinets, a heat exchanger istypically added by designing a replacement door with the heat exchangerfactory-mounted to the replacement door. A service technician thenremoves the original door from the legacy cabinet and mounts the newheat exchanger door in its place.

Referring again to FIG. 1, electronics cabinet 100 also includes areplacement door 118A that has a large opening formed through door 118A,and a heat exchanger 120 that sits entirely within the opening. Whendoors 118 and 118A are closed, base plate 110, top plate 112, and sidewalls 114 form an enclosure that has an air tight and water tight seal.

However, replacing an entire door for the sole purpose of adding a heatexchanger presents several problems. First, a substantial engineeringeffort is required to reverse-engineer a replacement door to perfectlyreplace the original door when the replacement door includesmodifications for a heat exchanger. Further, there are scores ofdifferent legacy electronics cabinets in existence which, in turn, wouldeach require the same substantial engineering effort.

Second, when a heat exchanger is added to the door, the heat exchangersits within the large opening, and thereby protrudes a few centimeters(inches) into the interior of the electronics cabinet. Depending on thecabinet design, this protrusion into the interior of the cabinet caninterfere with the internal equipment, complicating the design of thereplacement door.

Third, replacing the door also means replacing the main seal surface forthe cabinet. All electronics cabinets that house telecommunicationequipment must undergo rigorous testing before deployment. Replacing theoriginal door with a non-factory door invalidates several of theoriginal tests. As a result, the replacement door must be re-certifiedto work with the electronics cabinet. The recertification, however, canbe relatively expensive, and must be performed for each type ofelectronics cabinet.

Theoretically, rather than using a replacement door, a heat exchangercan be added to the original door in the field by a service technician.Practically, however, the process of field installing a heat exchangerin the original cabinet door is a difficult and time consuming process.

First, a very large rectangular opening must be cut out of the door,ranging from 50%-90% of the area of the door, along with dozens ofmounting openings that surround the rectangular opening. Once therectangular and mounting openings have been formed, dozens of mountingstuds must then be connected to the mounting openings and the heatexchanger to complete the mechanical portion of the installation.

Thus, there is a need for an approach to removing heat from legacyelectronics cabinets that does not require that the cabinet door bereplaced, and can be installed in substantially less time than the timecurrently required to complete a field installation of an air-to-airheat exchanger, such as heat exchanger 120.

SUMMARY OF THE INVENTION

The present invention provides an electronics cabinet that has anair-to-air heat exchanger mounted to the outside of the cabinet, and amethod of installing the heat exchanger that substantially reduces theamount of time required to install the heat exchanger in the field. Inaccordance with the present invention, an electronics cabinet includes abottom surface, a top surface, and a plurality of side wall surfacesthat are connected to the bottom surface and the top surface.

Further, the electronics cabinet includes a door that is connected to aside wall surface, and a heat exchanger mounted to an exterior surfaceof the electronics cabinet. When the door is closed, the bottom surface,top surface, side wall surfaces, and door form an air tight and watertight enclosure.

The present invention also includes a method of installing a heatexchanger in an electronics cabinet. The method includes the steps ofidentifying a mounting region on the exterior surface of an electronicscabinet to mount the heat exchanger, and placing a template on themounting region. The method also includes the steps of forming a firstopening and a spaced apart second opening that extend through theexterior surface into an interior region of the electronics cabinet, andmounting a heat exchanger to the electronics cabinet.

A better understanding of the features and advantages of the presentinvention will be obtained by reference to the following detaileddescription and accompanying drawings that set forth an illustrativeembodiment in which the principles of the invention are utilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a prior-art electronicscabinet 100.

FIG. 2 is a perspective view illustrating an example of an electronicscabinet 200 in accordance with the present invention.

FIG. 3 is a perspective view illustrating an example of an electronicscabinet 300 in accordance with the present invention.

FIG. 4 is a flow chart illustrating an example of a method 400 ofinstalling an air-to-air heat exchanger in accordance with the presentinvention.

FIG. 5 is a diagram illustrating an example of a template 500 inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a perspective view that illustrates an example of anelectronics cabinet 200 in accordance with the present invention. Asdescribed in greater detail below, the present invention eliminates thedifficulties normally associated with retrofitting an existing cabinetto include an air-to-air heat exchanger by attaching the heat exchangerto the exterior of the cabinet.

As shown in FIG. 2, cabinet 200 includes a bottom surface 210, a topsurface 212, a number of side wall surfaces 214, including a mountingside wall surface 214A, that are connected to bottom surface 210 and topsurface 212, and a door 216 that is connected to a side wall surface 214via hinges or other structures that allow an interior of cabinet 200 tobe exposed.

When door 216 is closed, the interior of cabinet 200, as defined bybottom surface 210, top surface 212, side wall surfaces 214, and door216, becomes an air tight and water tight enclosure. In addition,cabinet 200 includes a rack 218 that lies inside cabinet 200 and holdstelecommunication equipment 218A.

In accordance with the present invention, mounting side wall surface214A of cabinet 200 includes one or more air inlet openings 220A thatextend through mounting side wall surface 214A, and one or more air exitopenings 220B that also extend through mounting side wall surface 214A.The FIG. 2 example illustrates three air inlet openings 220A that eachhave a diameter of, for example, 8.890 cm (3.50 inches), and one airexit opening 220B that has a diameter of, for example, 13.335 cm (5.25inches).

As described in greater detail below, the hot air in cabinet 200 ispulled out of cabinet 200 through air exit opening 220B, while coolerair is discharged into cabinet 200 through the air inlet openings 220A.(Alternately, the hot air can be pulled out of cabinet 200 throughopenings 220A and discharged back into cabinet 200 through opening220B.)

In addition, mounting side wall surface 214A includes a number of firstmounting holes 220C that extend through mounting side wall surface 214Aaround the air inlet openings 220A, and a number of second mountingholes 220D that extend through mounting side wall surface 214A aroundair exit opening 220B. The first and second mounting holes 220C and 220Dcan have diameters of, for example, 0.635 cm (0.25 inch).

In further accordance with the present invention, cabinet 200 includes agasket 230, a gasket 232, and an air-to-air heat exchanger 234. Gasket230 has a first air opening 230A that extends through gasket 230 andsurrounds the number of air inlet openings 220A that are formed inmounting side wall surface 214A, and a number of first mounting holes230B that extend through gasket 230 and correspond with the number offirst mounting holes 220C that are formed in mounting side wall surface214A.

Gasket 232 has a second air opening 232A that extends through gasket 232and surrounds the number of air exit openings 220B that are formed inmounting side wall surface 214A, and a number of second mounting holes232B that extend through gasket 232 and correspond with the number ofsecond mounting holes 220D that are formed in mounting side wall surface214A. Gaskets 230 and 232 can both be implemented with, for example,silicon rubber gaskets.

Air-to-air heat exchanger 234, in turn, includes a back plate 240, afront plate 242, and a number of side walls 244 that are connected tofront plate 240 and back plate 242. Back plate 240 has a number of airexit openings 240A (one is shown in the example) that accommodates thenumber of air inlet openings 220A in mounting region 220.

In the FIG. 2 example, air exit opening 240A has a height that isslightly larger than the diameter of an air inlet opening 220A. Inaddition, air exit opening 240A has a width that is greater than 3× thediameter of an air inlet opening 220A (since three air inlet openings220A are shown in the FIG. 2 example).

In addition, back plate 240 has a number of air inlet openings 240B (oneis shown in the example) that accommodates the number of air exitopenings 220B in mounting region 220. In the FIG. 2 example, air inletopening 240B has a diameter that is substantially equal to the diameterof air exit opening 220B.

Further, back plate 240 has a number of first mounting holes 240C thatextend through back plate 240 around the air exit openings 240A, and anumber of second mounting holes 240D that extend through back plate 240around air inlet opening 240B. The first and second mounting holes 240Cand 240D can have diameters of, for example, 0.635 cm (0.25 inch).

In addition, although not shown in FIG. 2 (see FIG. 3), front plate 242includes a number of air inlet openings and a number of air exitopenings. Heat exchanger 234 can be implemented with a conventionalair-to-air heat exchanger, such as the air-to-air heat exchangerdescribed in U.S. patent application Ser. No. 10/692,393 filed on Oct.23, 2003, which is hereby incorporated by reference.

As shown in FIG. 2, air-to-air heat exchanger 234 is mounted to mountingside wall surface 214A of cabinet 200 via gaskets 230 and 232 and anumber of fasteners that pass through all or portions of first mountingholes 220C, 230B, and 240C, and through all or portions of secondmounting holes 220D, 232B, and 240D. The fasteners can be implementedwith, for example, #10 10-32 metal mounting screws and #10 flat headmounting washers.

In operation, hot air from the telecommunication equipment 218A rises tothe top of the enclosure, where a fan in air-to-air heat exchanger 234pulls the hot air into heat exchanger 234 via air exit opening 220B. Asthe air passes through heat exchanger 234, the air transfers heat to oneside of a cooler common metal wall in heat exchanger 234. The cooler airis then exhausted into cabinet 200 via the air inlet openings 220A.

At the same time, a stream of external air is pulled in from the outsidethrough the air inlet opening in front plate 242 via a fan in air-to-airheat exchanger 234, and across an opposite side of the common metal wallwhere heat from the common metal wall is transferred to the cooleroutside air. The warmer air is then exhausted back outside via the airexit opening in front plate 242.

Although FIG. 2 illustrated air-to-air heat exchanger 234 mounted to aside wall 214, heat exchanger 234 can alternately be mounted on othersurfaces, such as door 216. FIG. 3 shows a perspective view thatillustrates an example of an electronics cabinet 300 in accordance withthe present invention.

Electronics cabinet 300 is similar to electronics cabinet 200 and, as aresult, utilizes the same reference numerals to designate the structureswhich are common to both cabinets. As shown in FIG. 3, electronicscabinet 300 differs from electronics cabinet 200 in that cabinet 300utilizes a number of heat exchangers 234 (two in the FIG. 3 example),and mounts the heat exchangers 234 on door 216 rather than the sidewalls 214.

FIG. 3 also shows a number of air inlet louvers 310 that cover the airinlet openings of front plate 242, and a number of air exit louvers 312that cover the air exit openings of front plate 242. As shown in FIG. 3,the air inlet louvers 310 (and thereby the air inlet openings) lie abovethe air exit louvers 312 (and thereby the air exit openings). One of theadvantages of this arrangement is that by having the air inlet louvers310 above the air exit louvers 312, the hot exhaust air is kept frommixing with the cool intake air. (Otherwise, the hot exhaust air wouldblow directly over the air inlet louvers.)

FIG. 4 shows a flow chart that illustrates an example of a method 400 ofinstalling an air-to-air heat exchanger in accordance with the presentinvention. As shown in FIG. 4, method 400 begins at step 410 byidentifying a mounting region on the exterior surface of an electronicscabinet to mount the heat exchanger. The air-to-air heat exchanger canbe mounted to any accessible surface of the electronics cabinet (wherethe mounting screws can be accessed from the interior of the cabinet).

From an installation perspective, the air-to-air heat exchanger is bestlocated on a door due to the easy access that a door provides to boththe exterior and interior sides of the cabinet. From a performanceperspective, the inlet and exit openings, such as the air inlet openings220A and air exit opening 220B, are best located so that the air inletopenings are located above the air exit opening.

The electronics cabinet, such as cabinet 200, has a small temperaturegradient from the top to the bottom of approximately 2° C.-3° C. As aresult, by pulling the hot air out of the cabinet into the heatexchanger through air exit opening 220B, and discharging the cooler airinto the cabinet through the air inlet openings 220A, the coolerdischarged air helps to dilute the warmer air at the top of the cabinet.

In addition, better results can be obtained by mounting the heatexchanger on east or north facing sides in the northern hemisphere toreduce the amount of direct afternoon sunlight, and as high as possibleon the electronics cabinet, or near heat generating devices such aspower rectifiers, to circulate the warmest air.

The heat exchanger should also be mounted to a flat, smooth surface toinsure the gaskets seal properly. Further, better results can beobtained if there is an unobstructed air flow between the internaltelecommunication equipment, such as equipment 218A, and the air inletsand exits, such as the air inlets 220A and air exit 220B of, forexample, approximately 10.16 cm to 15.24 cm (4 to 6 inches).

Once a mounting region has been identified, such as on a side wall 214or a door 216 of cabinet 200, method 400 moves to step 412 to clean thesurface of the mounting region. The mounting surface must be clean tomake a water tight seal against the silicon rubber gaskets on the heatexchanger.

Following this, method 400 moves to step 414 to place a template on themounting region. FIG. 5 shows a diagram that illustrates an example of atemplate 500 in accordance with the present invention. As shown in FIG.5, template 500 includes a number of air inlet openings 510 thatcorrespond with the centers of the to-be-formed air inlet openings, suchas openings 220A, and a number of first mounting openings 512 thatcorrespond with the number of to-be-formed first mounting holes, such asmounting holes 220C.

In addition, template 500 includes a number of air exit openings 514(one is shown in the example) that correspond with the centers of theto-be-formed air exit openings, such as opening 220B, and a number ofsecond mounting openings 516 that correspond with the number ofto-be-formed second mounting holes, such as mounting holes 220D. In theFIG. 5 example, openings 510, 512, 514, and 516 are the same size. Towork with the FIG. 2 example, template 500 has three air inlet openings510 and one air exit opening 514.

Returning to FIG. 4, once the template has been placed on the exteriorsurface, method 400 moves to step 416 to drill pilot holes in theexterior surface of the electronics cabinet through the template. Thepilot holes, which can have a diameter of, for example, 0.308 cm (0.125inch), are best drilled from the outside in to protect the gaskets fromany rough edges due to the drilling.

The pilot holes include a number of drilled air inlet openings thatcorrespond with the centers of the to-be-formed air inlet openings, suchas openings 220A, and a number of drilled first mounting openings thatcorrespond with the number of to-be-formed first mounting holes, such asholes 220C. In addition, the pilot holes also include a drilled air exitopening that corresponds with the center of the to-be-formed air exitopening, such as opening 220B, and a number of drilled second mountingopenings that correspond with the number of to-be-formed second mountingholes, such as holes 220D.

After the pilot holes have been drilled, method 400 moves to step 418 toremove the template, and then to step 420 to drill out the openings. Theopenings are drilled out by cutting, in any order, the drilled air inletopenings to form air inlet openings, such as openings 220A, the drilledair exit opening to form an air exit opening, such as opening 220B, andthe first and second drilled mounting openings to form first and secondmounting openings, such as openings 220C and 220.

The drilled air inlet openings are cut out to have a diameter of, forexample, 8.890 cm (3.50 inches). The drilled air exit opening is cut outto have a diameter of, for example, 13.335 cm (5.25 inches). The firstand second drilled mounting openings have a diameter of, for example,0.635 cm (0.25 inch). Following the cutting, the hole edges are filedand deburred and the surface is wiped clean of any metal fragments.

Next, method 400 moves to step 422 to mount an air-to-air heatexchanger, such as heat exchanger 234, to the electronics cabinet. Theheat exchanger is mounted by aligning the holes of the heat exchangerwith the holes in the mounting surface of the cabinet, and then feedingthe electrical cables, such as power and alarm cables, through one ofthe openings into the interior of the cabinet.

Following this, the fasteners, such as #10 10-32 metal mounting screwsand #10 flat head mounting washers, are threaded through all of thefirst mounting holes, such as the first mounting holes 220C, 230B, and240C. Similarly, the fasteners, such as #10 10-32 metal mounting screwsand #10 flat head mounting washers, are also threaded through all of thesecond mounting holes, such as the second mounting holes 220D, 232B, and240D. All screws should be threaded before any of the screws aretightened, and the holes should be aligned to avoid stripping. One ofthe advantages of the present invention is that, because of the rigidityprovided by the heat exchanger, the present invention tends to stiffenthe door when the heat exchanger is mounted to a door.

Once the heat exchanger has been mounted to the mounting region, method400 then moves to step 424 to connect the electrical cables tocorresponding cables within the electronics cabinet. Method 400 of thepresent invention is complete when the electrical cables have beenconnected to cables within the electronics cabinet.

Thus, another of the advantages of the present invention is that themethod of the present invention greatly simplifies the process requiredto install an air-to-air heat exchanger in the field. The heat exchangercan be mounted to the electronics cabinets using as few as two mainround holes (inlet and exit), and a substantially fewer number ofmounting holes, based on a simple template.

Another advantage of the present invention is that since the heatexchanger can be easily installed in the field in a short amount oftime, heat exchangers can be installed without using a replacement door.As a result, a replacement door with a heat exchanger does not have tobe customized for every cabinet type. Further, since a cabinet door doesnot need to be replaced, all of the issues associated with replacing adoor are eliminated.

It should be understood that the above descriptions are examples of thepresent invention, and that various alternatives of the inventiondescribed herein may be employed in practicing the invention. Thus, itis intended that the following claims define the scope of the inventionand that structures and methods within the scope of these claims andtheir equivalents be covered thereby.

1. An electronics cabinet comprising: a bottom surface; a top surface; aplurality of side wall surfaces connected to the bottom surface and thetop surface; a door connected to a side wall surface, when the door isclosed, the bottom surface, top surface, side wall surfaces, and doorform an air tight and water tight enclosure; and a heat exchangermounted to an exterior surface of the electronics cabinet.
 2. Theelectronics cabinet of claim 1 wherein the exterior surface of theelectronics cabinet includes: a cabinet air exit opening that extendsthrough the exterior surface into the enclosure; and a cabinet air inletopening that extends through the exterior surface into the enclosure,the cabinet air inlet opening being spaced apart and separated from thecabinet air exit opening.
 3. The electronics cabinet of claim 2 whereinthe cabinet air inlet opening lies above the cabinet air exit opening.4. The electronics cabinet of claim 2 wherein the heat exchangerincludes: a first air inlet opening that pulls in a first stream of air,the first air inlet opening being substantially aligned with the cabinetair exit opening; and a second air inlet opening that pulls in a secondstream of air.
 5. The electronics cabinet of claim 4 wherein the heatexchanger includes: a first air exit opening that exhausts the firststream of air, the first air exit opening being substantially alignedwith the cabinet air inlet opening; and a second air exit opening thatexhausts the second stream of air.
 6. The electronics cabinet of claim 5wherein the second air inlet opening lies above the second air exitopening.
 7. The electronics cabinet of claim 6 wherein the first streamof air and the second stream of air are never mixed with each other. 8.The electronics cabinet of claim 6 wherein the first stream of air andthe second stream of air contact opposite sides of a common wall.
 9. Theelectronics cabinet of claim 2 wherein the exterior surface is a sidewall surface.
 10. The electronics cabinet of claim 2 wherein theexterior surface is a region of a door.
 11. A method of installing aheat exchanger in an electronics cabinet, the method comprising thesteps of: identifying a mounting region on the exterior surface of anelectronics cabinet to mount the heat exchanger; placing a template onthe mounting region; forming a first opening and a spaced apart secondopening that extend through the exterior surface into an interior regionof the electronics cabinet; and mounting a heat exchanger to theelectronics cabinet.
 12. The method of claim 11 wherein the heatexchanger includes a third opening that is substantially aligned withthe first opening, and a fourth opening that is substantially alignedwith the second opening, the third and fourth openings being spacedapart.
 13. The method of claim 11 wherein the forming step includes thestep of drilling a plurality of pilot holes in the exterior surface ofthe electronics cabinet through the template.
 14. The method of claim 13wherein the forming step further includes the steps of: drilling thefirst opening using a first pilot hole; and drilling the second openingusing a second pilot hole.
 15. The method of claim 14 wherein the secondhole is larger than the first hole.